1. Field of the Invention
The present invention concerns a system of receiving signals, particularly DVB-T (Digital Video Broadcasting-Terrestrial) signals, comprising a retransmission base to amplify the signals captured at a point in a domestic environment and retransmit them at the same frequency to digital receivers of the said domestic environment. The invention particularly relates to Digital Terrestrial Television (DTT).
2. Related Art
The modulation used for the transmission of DVB-T signals is OFDM modulation. This modulation is particularly robust to echoes and makes possible the retransmission of a DVB-T channel at the same frequency in a domestic environment. Thus DVB-T signals can be captured at a point in the environment where they are at a sufficient level and then amplified and retransmitted in the environment to be captured at all points of the said environment by “portable” digital receivers such as digital television sets or analogue television sets with digital terrestrial decoders. This is the principle that has been adopted for Digital Terrestrial Television (DTT). DVB-T signals are captured with an antenna preferably placed outside the home, are reamplified and then retransmitted inside the home.
However, this principle poses feasibility problems. It is currently not feasible to retransmit the totality of the DVB-T signal receive band without risking interference to devices (primarily analogue television receivers) using common frequency bands in the same domestic environment or in a nearby domestic environment. The reamplification of the whole band could in effect cause echoes destroying the analogue reception around the retransmitter and creating intermodulation problems.
Amplification must apply only to the broadcast digital channels. So amplification must be selective. However, it is very difficult to produce a “universal” system that amplifies only the broadcast digital channels. Their number and position in the frequency band vary from one country or region to another. In addition, they are likely to increase significantly in number when analogue broadcasts disappear. So, at the moment, it is not possible to provide the number of amplifiers necessary to produce such a “universal” system.
Currently, the favoured solution consists in amplifying a single channel that is chosen dynamically by the user. This solution however requires the provision of at least one retransmitter for each portable digital apparatus in the home. If the user wants to watch two programmes at the same time on two separate channels, the one being displayed on the television's full screen and the other in a screen window, two retransmitters need to be provided for one receiver. If the user at the same time also wants to record a programme on another channel, three are required. This solution is therefore particularly costly in terms of equipment.